1. Field of the Invention
This invention relates to the storage of energy for future use, and more particularly, to apparatus and a method for converting electrical energy during off-peak periods of low demand to hydrogen and oxygen that are stored for later conversion back into electrical energy during peak periods of high demand. It also relates to such a system and method that operates at self generated high pressure for efficient energy conversion and storage of the gases.
2. Background Information
Electric utilities have large installed capacity to met peak demand and the required safety margin. Most of the time, especially at night and weekends, only a fraction of that capacity is required to meet nominal demand. In fact, some of the peaking units operate only a few hours a year. In addition, utilities purchase blocks of peak power on a take-or-pay basis to ensure sufficient power during their highest demand periods, such as mid-summer heat waves. In some instances, bottlenecks in the transmission system complicate the task of delivering power where it is needed during periods of peak demand.
In addition to the problems associated with economically meeting peak demand, utilities have endeavored to improve performance through load leveling in order to operate certain of their equipment at maximum efficiency. U.S. Pat. No. 6,093,306 describes a complex system for abating emissions and providing load leveling for fossil fuel plants. The process produces hydrogen through the electrolysis of water during off-peak periods for use in a fuel cell at the plant to generate electricity during peak periods, which is added to the plant output. While this allows the fossil fuel plant to operate more efficiently and cleanly, it does not address the problems of transmission constriction or peaking.
It has also been suggested that renewable energy sources, such as solar and wind energy, can be used to generate hydrogen gas which is then used to generate electricity in fuel cells during periods when the sunlight or wind is not available or insufficient to produce electricity. Again, neither of these approaches address the problems of transmission restriction or peaking.
There is room, therefore, for improvements in the configuration and operation of systems for generating and distributing electric power.
In accordance with the invention, electric energy generated by a primary electric power source is transmitted to a specified location remote from a utility generating station where it is stored by using it to disassociate water into hydrogen and oxygen, which are stored for later conversion of at least the hydrogen into locally generated electricity in a hydrogen to electricity converter. The utility generated electricity is wheeled to the specified location, such as a user site, a substation, or on a distribution line during off-peak periods and the stored gases are used to produce the locally generated electricity during peak periods. Thus, the low cost power generated by the utility during low demand periods can be converted to higher value electric power during peak periods. In addition, the adverse effects of constriction on the transmission system are ameliorated by reducing the transmission capacity required during peak demand periods. This advantage is enhanced by wheeling the utility generated power during low demand periods to a plurality of distributed specified locations remote from the utility generating station. Also, by providing distributed generation using stored gas, the effects of transmission interruptions, such as for example by storms, are mitigated.
As another aspect of the invention, the apparatus which generates the deferred electric power comprises an electrolyzer energized by the primary electric power source to disassociate water into hydrogen and oxygen, and a gas collection system that includes a first gas-water column connected to the electrolyzer to form a first flow loop in which the hydrogen produced in the electrolyzer passes to the first gas-water column and forces water from the first gas-water column into the electrolyzer. This gas collection system further includes a second gas-water column connected to the electrolyzer to form a second flow loop in which oxygen produced in the electrolyzer passes to the second gas-water column and forces water from the second gas-water column into the electrolyzer. A gas storage system stores the hydrogen from the first flow loop and the oxygen from the second flow loop. A hydrogen to electricity converter, such as fuel cell or combustion engine driven generator, converts the stored hydrogen back into electricity using either the stored oxygen or ambient oxygen. In the later case, the collected oxygen can be utilized or sold for other purposes. A valving system maintains the pressure of the hydrogen and oxygen at a selected pressure above about 1,000 psi by controlling the flow of hydrogen from the first flow loop and oxygen from the second flow loop to the gas storage system. Thus, the apparatus operates at high pressure without additional pressurizing equipment for efficient conversion and gas storage. This pressure can be regulated to between about 2,500-5,000 psi with the exemplary apparatus operating at about 3,000 psi.